Just watched A New Hope on TV and noticed what I think is a new continiuity error.
In the Droid sale scene, when the red R2 unit (R4-D5 I think) rolls of and then blows it's motivator luke calls out to Uncle Owen "What about the blue one?" The shot shifts back to R2 D2 and you can see the red R2 unit still next to him. Then it shifts back to Luke and the smoking R2 unit has shifted back.
This was in the Special Edition as screen on Sky Premier. Not sure if this has always been there or is only in the SE's that the mistake appears.
The scene was devised differently originally I think. That's why there's this continuity error. I think Luke wanted to pick the blue one first, but Owen felt it was too beat up so he picked the nicer looking one. They probably didn't make a proper shot of R2 for this alternative cut.
Well there is that. The toy however was labelled R5D4. Anyway as to the what was on screen maybe they had more than one R5 unit and having seen one blow wasn't gonna risk another. As for names maybe Luke just aint that bright when it comes to Droid names or classifications and refers to them under a single banner label...